Neural organization and neural responses in mammalian retinas are investigated using electrophysiological, optical, and pharmacological techniques: (1)GABA- and glutamatergic responses were recorded from dissociated rat rod bipolar cells (rb's) and other dissociated rat retinal neurons (round cells) using oxonol, a fluorescent, potentiometric dye. Fluorescence signals simultaneously recorded from dendrites, cell bodies, and in a few cases, axon terminals of rod-bipolar cells superimposed well. GABA (25 microM) decreased fluorescence (about 0.1 log unit) signaling hyperpolarization in both rb's and round cells, with bicuculline blockade evident in about 20% of cases. Kainic acid (50 microM) decreased fluorescence, signaling hyperpolarization in rb's, while in round cells fluorescence often increased (about 0.5 log unit), signaling depolarization. Both effects were blocked by CNQX. Gramicidin, which depolarizes all cells to near 0 mV, increased fluorescence by 0.5 log units in both rb's and round cells. Fluorescence signals resembled those expected of voltage records. (2) Light-evoked noise in ON alpha-ganglion cells has been studied in a flat-mount, superfused cat retina. In this preparation, electrodes are aimed under visual control at alpha ganglion cells, and penetration is verified by immediate staining of impaled cells with pyranine dye. After TTX (20 nM) blockade of impulse activity, maintained, light-evoked, depolarizing generator potentials were observed, together with increased voltage variance (noise). Stepped applications of CNQX (1-10=E6M) reduced both generator potential and associated noise variance in a manner indicating that quantal event size was also reduced. This suggests that some alpha ganglion cell dark noise, and nearly all light evoked noise, arises from glutamate quantal packets impinging directly on ganglion-cell dendrites. (3) The neural circuitry of ON-OFF amacrine cells in cat retina was studied electrophysiologically and ultrastructurally with HRP-filled microelectrodes. Stained cells were of multiple types; however, all dendritic arborizations were monostratified and consisted of two zones: a central zone of dendritic branching, and a more distal zone of multiple axon-like processes. Gaussian receptive fields were larger than central dendritic zone diameters. Reversal potentials for both ON and OFF components were positive to resting potentials. Input from amacrine and one or more cone-bipolar cell types and output onto ganglion cells was noted.